A type of thrust bearing has been known in which a bearing member having spiral grooves is employed to bear against a flat member such as to suspend a thrust load by the fluid dynamic pressure produced between the flat member and the surface having the spiral grooves when the two members are caused to rotate relative to each other. One of such examples is disclosed in U.S. Pat. No. 4,575,264. The thrust bearing disclosed in said U.S. patent is quite satisfactory in its operation and its excellency is admitted in the following points, namely, the dimension thereof being made compact; a special cooling means being unnecessary due to the presence of fluid surrounding the bearing; dynamic pressure serving to minimize the friction loss; power loss being greatly reduced say to 1/5 of the power required in the conventional tilting pad-type thrust bearing; and capable of bearing the thrust load in the direction of either type of rotation (normal and reverse). However, the thrust bearing disclosed in the above U.S. patent is usually limited for use in a vertical shaft and within water or liquid such as for a submersible motor and/or pump since the dynamic pressure is produced in the presence of water or liquid. Also, the thrust bearing of prior art has been supplied as a bearing already installed in a certain piece of equipment and, thus, such bearing has not been in a form that the bearing itself could be made independently available for use in various applications.
Also, the spiral element of prior art which has spiral grooves on its opposite side surfaces is arranged to be freely disposed between a stationary member and a rotatable member and, thus, it has been necessary to provide some means to prevent radial displacement of the spiral element. However, even with the provision of such means for preventing radial displacement, the thrust bearing of prior art has not been capable of being used in a horizontal shaft because the spiral element may interfere with the means for preventing radial displacement if such thrust bearing is to be installed in the horizontal shaft.
Further, another type of thrust bearing (so-called "hybrid type") is available which also utilizes fluid dynamic pressure derived from the relative rotation between an element having a spirally grooved surface and a flat element. An example of such an improved spiral groove thrust bearing of the hybrid type is disclosed in Japanese Patent Public Disclosure No. 74132/82. The hybrid type spiral groove thrust bearing disclosed in this Disclosure employs a steel ball embedded in a spiral groove element such that the steel ball protrudes a slight distance above the surface of the spiral element. This protruded portion of the ball serves as a pivot where the bearing is not being rotated. This type of bearing may serve to function as intended; however, the quite minor dimension of the protrusion needs to be precisely controlled so that such protruded distance is smaller than the clearance between the spiral element and the opposing surface when the fluid dynamic pressure is generated during the relative rotation therebetween. So manufacturing of this type of bearing is quite difficult. Further, this type of bearing may not be able to prevent radial displacement of the spiral element. Also, the ball would be subjected to repeated impact during stoppage and reversing of the rotational direction so that the protruded portion of the ball may be damaged whereby the function of the pivot is easily impaired. Because of the recognition that the thrust bearing proposed in the U.S. patent referred to above exhibited remarkable advantages compared to the thrust bearing of other types and also because of the difficulties encountered in the hybrid type disclosed in the above Disclosure, there has been a desire to have a thrust bearing enjoying substantially all of the advantages offered by the type disclosed in the above U.S. patent but free from the limitations or difficulties imposed thereon, such as application only to vertical shafts in the submerged state and the difficulties encountered in manufacturing, etc.